<form method="post">

  <select id="centro_costos" name="centro_costos" style="">
    <?php foreach ($centros_de_costo as $centro_costos): ?>
    <option id="opt_centro_costos" value="0"></option>
    <option id="opt_centro_costos"><?php echo $centro_costos->getNombre(); ?></option>
    <?php endforeach; ?>
</select>

    <input type="submit"  value=" enviar ">
</form>
  <br/><br/><br/>

  <?php echo $centro ?>
